Cisco Nexus 3000 and 9000 Series Border Gateway Protocol Denial of Service Vulnerability
Summary
| CVE | CVE-2026-20171 |
|---|---|
| State | PUBLISHED |
| Assigner | cisco |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-05-20 17:16:19 UTC |
| Updated | 2026-05-20 17:30:40 UTC |
| Description | A vulnerability in the Border Gateway Protocol (BGP) enforce-first-as feature of Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, remote attacker to trigger BGP peer flaps, resulting in a denial of service (DoS) condition. This vulnerability is due to incorrect parsing of a transitive BGP attribute. An attacker could exploit this vulnerability by sending a crafted BGP update through an established BGP peer session. If the update propagates to an affected device, it could cause the device to drop the BGP session and flap with the BGP peer that is forwarding this update, resulting in a DoS condition. |
Risk And Classification
Primary CVSS: v3.1 6.8 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
EPSS: 0.000390000 probability, percentile 0.120260000 (date 2026-05-27)
Problem Types: CWE-670 | CWE-670 Always-Incorrect Control Flow Implementation
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Primary | 6.8 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H |
| 3.1 | CNA | CVSSV3_1 | 6.8 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
ChangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(1) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(1q) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(2) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(3) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(3t) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(2a) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(1) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(4) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(2) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(5) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(3v) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(1) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(99w) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(6) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3w) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(99x) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3o) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(4) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3p) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(4a) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(2) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3q) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(5) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(7) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(3) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3x) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(4g) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(1) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(8) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(3r) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(6) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(4) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(4h) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(2) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(7) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(5) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(3) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.2(9) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(4g) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.6(1) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(3t) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.3(8) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.4(6) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(3s) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(3e) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(3o) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.6(1s) | Not specified |
| CNA | Cisco | Cisco NX-OS Software | affected 10.5(3p) | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-ie... | [email protected] | sec.cloudapps.cisco.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
Additional Advisory Data
Exploits
CNA: The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
There are currently no legacy QID mappings associated with this CVE.